Low-grade heat, which is typically considered less than 100 degrees, represents a significant waste energy stream in industrial processes, power generation and transport applications. Recovery and re-use of such waste streams is desirable. An example of a technology which has been proposed for this purpose is a Thermoelectric Generator (TEG). Unfortunately, TEGs are relatively expensive. Another largely experimental approach that has been proposed to recover such energy is the use of Shape-memory Alloys.
A Shape-memory Alloy (SMA) is an alloy that “remembers” its original, cold-forged shape which once deformed returns to its pre-deformed shape upon heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems.
The three main types of Shape-memory Alloys are the copper-zinc-aluminium-nickel, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys but SMAs can also be created, for example, by alloying zinc, copper, gold and iron.
The memory of such materials has been employed or proposed since the early 1970's for use in heat recovery processes and in particular by constructing SMA engines which recover energy from heat as motion. Recent publications relating to energy recovery devices include PCT Patent Publication number WO2013/087490, assigned to the assignee of the present invention. It is desirable to translate the contraction of the SMA or NTE material into a mechanical force in an efficient manner. It is not a trivial task and generally is complicated and involves significant energy losses, as disclosed in patent publication numbers DE3014560 and US2008/034750. A problem with the systems disclosed is that they do not take account of the time of reaction of each core for power production such that the cycle time between heating and cooling of cores can take a long time resulting in inefficient operation. Consequently much of the energy in the working fluid is wasted between heating cycles.
It is therefore an object to provide an improved system and method in an energy recovery device.